1. Field of the Invention
This invention relates to tool holding devices and more particularly to quick change tool holders of the collet type.
2. Prior Art
Collets have long been used for attaching tools to machine spindles. More recently, particularly with the development of large machine tools, it has been a common practice to interpose a tool holder between the collet and the tool such that a collet affixed to a machine spindle engages a tool holder affixed to the tool.
More recently, quick change tool assemblies have become widespread where the collet is designed to be quickly disengaged to release the tool holder. Finally, in order to allow variance in the projection of the tool holder from the collet, it has been known to provide the tool holder with an adjustable position nut which then becomes the gripping point between the collet and the tool holder.
The gripping members of the collet can be, variously, axially extending circumferentially spaced spring fingers or circumferentially spaced balls radially moveable under the influence of caming surfaces. See for example U.S. Pat. No. 3,790,182. One problem experienced in association with such prior art devices arises from the fact that in order for the quick release features to properly function, it is necessary that the gripping members, whether fingers or balls, completely release the nut upon actuation of the collet release means. However, since the tools are universally used in environments which quickly become polluted during the use of the tool, it is easy for foreign matter, particularly over prolonged periods of use, to invade the assembly. This problem is aggravated when the tool is being operated in an environment requiring the application of a stream of coolant fluid. In such instances, it is possible for the gripping members to become gummed or fouled to an extent that they do not properly release. When this occurs, the entire assembly may have to be removed from the machine tool spindle and be subject to an external cleaning operation in order to free the tool holder from the collet. This problem is aggravated because, typically, the gripping members are operated extremely axially close to the end of the collet assembly, and therefore in proximity to the working environment of the tool.
A further disadvantage with the prior art designs lies in the fact that frequently the nut can provide a fulcrum point about which the tool holder can tend to tilt in the collet assembly. This is particularly true where the tool holder nut is engaged by a circumferential portion of the collet assembly.
It would therefore be an advance in the art to provide a quick change collet tool holder of the type utilizing an adjustable tool holder nut held in working relationship with a machine spindle by engagement of the nut by gripping members carried by a collet assembly affixed to the spindle where the interior of the collet assembly is sealed. It would be another advance in the art to provide such an assembly where any tendency of the nut to allow tilting of the tool holder is substantially reduced or eliminated.